This invention relates generally to couplers for tubes carrying highly pressurized fluids and particularly to high pressure liquid chromatography column and tube couplers. Still more particularly, this invention relates to cartridge columns for high pressure liquid chromatography.
Liquid chromatography is used for chemical analysis and for chemical product isolation or purification. A porous material is held stationary within a chamber, such as a relatively long column, and a mobile liquid material is forced through the porous material. Typically the porous material is an inert powder with a chemically modified surface. The mobile liquid comprises a carrier liquid and other dissolved chemical substances into which a sample is injected for separation into its components. The components of the sample have varying affinities for the stationary porous material. Therefore, as the mobile liquid moves through a chromatographic column, the chemical substances experience delays that are functions of their affinities for the stationary porous material.
The column separates the chemical substances into layers or zones that emerge from the column at different times. The emergence of each substance from the column is detected by a refractometer, an ultra-violet light, an absorbtometer or other suitable analytical apparatus through which the mobile liquid flows after leaving the column.
The useful life of a column may be greatly shortened by particles or chemical contaminants in the mobile liquid or in the sample input to the column. These contaminants can be trapped in a small, inexpensive precolumn connected in series upstream from the analytical column. When performance of the chromatographic system has deteriorated, the precolumn may be replaced to restore performance of the system. Previously available precolumn devices are either mechanically complex and therefore, difficult and expensive to manufacture or have deficiencies such as constrictions in the flow path that cause disturbances in the flow profile of the liquid stream.
Although it is possible to interconnect the analytical column and the precolumn with a length of capillary tubing and associated connectors, that method is expensive and introduces substantial extra mixing volume and other extra column effects. The analytical column and the precolumn are typically held within a holder body under compression by a pair of end caps. Normally capillary tubing is connected to the end caps and sealed thereto against conical seats in the ends of the end caps. The seats are subject to wear as the capillary tubing is connected and disconected so that the end caps must be periodically replaced.
Previous high pressure liquid chromatography tubing connectors introduce radical changes in the diameter of the flow path thereby forming spaces in which fluids from one part of the stream of mobile fluid can collect and then intermix with fluids from another part of the stream. Non-uniformity in the fluid flow between the precolumn and the analytical column is undesirable because it causes eddies and stationary regions within the mobile fluid, which impair the ability of the column to separate the mobile liquid into layers. An efficient analytical column will produce narrow, symmetric bands and will cause the detecting instrument to produce a sharp peak for each substance in the mobile liquid. Previous high pressure liquid chromatography systems cause distortion in the peak shape because the edges of the layers are asymmetrical. The detector produces an output signal peak each time a substance enters the detector, indicating incomplete separation of the chemical substances when the flow path includes eddies and dead spaces.